Electric conductor for signaling purposes



Dec. 31, 1929. U, MEYER 41,741,644

ELECTRIC CONDUCTOR FOR SIGNALING PURPOSES Filed June 5, 1926 Patented Dec. 31, 192

ULEILAS MEYER, 0F COLOGNE-MULHEIM, GERMANY, ASSIG-NOR T0 FELTON & GUIL- LEAUME CARLSWERK ACTIEN-GESELLSCHAFT, 0F GOLOGNE-MULHEIM, GERMANY ELECTRIC CONDUCTOR FOR SIGNALING PURJPSES Application filed .Tune 5, i926, Serial No. 113,922, and. in Germany July 9, 1925.

It has long been known that the damping of conductors can be reduced by surrounding the conductor with a magnetic Jmaterial, thereby increasing its self-inductance. The higher the permeability of the magnetic material with weak fields, the greater is the increase in self-inductance- At the same time however, with the same thickness of material the resistance producing a loss viz, the virtual resistance increases with the permeability, this increase being more rapid than the increase in permeability. As the saidresistance unfavourably affects the damping, the higher permeability does not always signify an improvement in the conductance. It has already been pointed out that owing to the relationship above referred to it is necessary to make the thickness of the layer of magnetie material as small as possible, but what exactly is to be understood by the term as small as possible has never been defined, that is to say, it has not been specifically stated as to how thick the magnetic layer should be, with any given permeability, in order to obtain the most satisfactory damp-- rihe present invention indicates how the damping of a conductor having a layer of magnetic material wound round it can be reduced to a minimum with'a given permeability of the material of the said layer. -In the accompanying drawings, Fig. 1 is a diagram showing the damping as a function of the thickness of the layer of magnetic material and of the permeability, whilst Figures 2.

200, 400, 1000 and 2000) other conditions being similar. As willA be seen, with increasing thickness4 of layer the damping at first decreases, for all permeabilities, and then increases under the infiuence of the increasing virtual resistance. While at the lower permeabilities, the lowest part of the curve is rather Hat with/increasing higher permeabilities the same is less and less flat. Thus, the higher the permeability the more impon tant it is to make the layer of the magnetic material of the correct thickness. The lack of knowledge as regards the suitable ratio between permeability and thickness of layer has retarded the employment of materialsof higher permeability (a 200) for signaling conductors. Such materials have not yet been used in connection with telephone cables but only in connection with telegraph cables with which the conditions are simpler in this respect, as the virtual resistance is lower at the low frequenciesl which are employed in telegraph work.

The present invention takes into consideration all essential factors and indicates for any shape of the magnetic layer the dimensions of the magnetic material corresponding to the minimum total damping for a definite permeability.

In the following discussion, arrangements of the loading material are compared with each other, which have similar geometrical forms, or to be more accurate, the cross sections of which in a plane passing through. the axis of the copper conductor, form geometrically similar figures.v This comprises single or multiple tape windings, wire .Windings (with or without air spacings) or any other arrangements. In Figure 2 a copper conductor a is provided with a winding of Wire band similarly in Figure 3, in the latter ligure the wire b being comparatively thinner. In both figures the surrounding wiring consists of a singlewire without intermediate spacing. In Figure 4 the wiring surrounding the conductor a consists of a Wire b With intermediate spacing o. In Figure 5 the conductora is wound with a single tape wiring b and in Figure 6 with a multiple tape wiring Z). i

The discussion will hereinafter be limited to one and the same arrangement, the arrangements Which are geometrica-ily similar cuiy to each other only diH'ering with respect to' the dimensions of the magnetic material used per unit length of the copper conductor..

More clearly expressed the arrangementsv differ from each other by the thickness d 0f\ their layers, d being understood to represent any dimension taken perp-:ndicularly to the outer surface ofthe conductor, for instance in the case of multiple tape windings (with or without intermediate air spacings) the diameteror any other dimension increasing proportionately therewith.

The approximation R 0 wtg 2 L 2v LU A holds for the damping of conductors under certain conditions existing in this'case, R being the total resistance, C the capacity, L the self-indutance (all per unit length) and a2/g8 the Well-known expression for' the leakance, i. e. the product of the angular frequency w and the tangent of the phase angle devi'ation 8 from 90, which is the phase angle for a perfect dielectricum. W ith Krarup conductors the total resistance R is equal to the sum of the resistance of the copper B0, the eddy current resistance p1, and the hysterises resistance p2. Now, as a first approximation, if windings with forms which are ge'ometrically similar (in the sense above described) are compared both L and p2 are proportional to the permeability u and the thickr ness of Ilayer d, While p1 is proportional to the square of ,L and the third power of d thus it can be stated L and p1 @M2653 and thus This i complicated equation is converted into a very much simpler'form by substituting again th`e magnitudes L1, p1, p2, whence the following is obtained tjvThus with Krarup conductors the minimum damping is obtained if the `thickness of'- layer is' such that five times the eddy current resistance plus the hysteresis resistance and plus the product of the angular frequency the angle corresponding to the losses and the .current resistance.

manera sclf-induetance are equal to the continuous As the above discussion isindependent ofthe precise form of the Krarupl surrounding winding, the result holds forany kind of surrounding winding. i That it also holds for multiple layers results from the fact that the partial self-inductance andV virtual resistance due to the individual llayers have additive effects, so that each individual layer can be considered in the same Way;

ln the case of telephone conductors w Lg and p2 are usually small as compared with R0, so that in this case the thickness of' layer of) the Krarup material (in the sense above described) must be such that the virtual resistance produced. -by eddy currents in the ferromagnetic material is approximately `equal to` a fifth of the continuous current resistance ofthe conductor. As the eddy current resistance is dependenton the frequency lit isnecessary to decide for what frequency -For w=5000, which represents in general the mean frequency of the telephone current, this would mean a very great distortion, as the damping Will be 1.5 times as great ai l i )ttl @ad aix/fragst@ ad with a value of w: 10000. 0n the other hand, an increase in the damping of this magnitude would be tolerable in most cases between 0:7000 and w=l4000. lt is thus advisable that therule should be applied for w=7000. If still smaller distortion is desired the basic frequency used in the calculation must be still higher.

By inserting a mean value for the loss constants of the magnetic material we obtain from the above rule for the usual sizes of telephone conductors the following approximate cond-itions for the suitable thickness of the individual layers of the Krarup material 1n mm.

As an example, the advisable limits for the thickness of layer under normal circumstances, for various permeabilitiesrare given in the'following table on the basis of the reinvention Permeability Thickness of layer 300 0.09 to 0.18 mm. 700 0.05 to 0.10

What I claim is 1. A conductor for signaling purposes having layers of ferro-magnetic material Wound round it for the purpose of increasing the self-inductance, the said ferro-magnetic material having an initial permeability greater than200, the thickness of the said layers being such that with the frequencies and current strengths which are employed for the said signaling purposes, the sum of iive times the eddy current resistance of the said layers plus the hysteresis resistance and plus the product of the angular frequency, the self-inductance and the tangent of the phasevangle deviation from 90 in the insulating material is approximately equal to the continuous current resistance of the said conductor. v

2. A conductor for telephone communication, having layers of ferro-magnetic'material Wound round it for the purpose of increasing the self-inductance, the said ferromagnetic material having an initial permeability greater than 200, the thickness of the said layers being such that, with the current strengths which are employed for the said communication and with an angular frequency of 7000, the virtual 'resistance is` approximately equal to one ifth of the continuous current resistance of the said conductor.

3. A conductor for signaling purposes having layers of ferro-magnetic material Wound round it for the purpose of increasing the self-inductance, the said ferro-magnetic material having an initial permeability greater than 200, the thickness of each individual layer of the ferro-magnetic material in mm. being for currents with an angular frequency of 7000 approximately equal to L aw/lf In testimony whereof I have signed my name to this specification.

ULFILAS MEYER. 

